Synthetic twines and method of production thereof



Dec. 29, '1970 J. A. KIPPAN 3,551,280

SYNTHETIC TWINES AND METHOD OF PRODUCTION THEREOF" Original Filed March 22, 1965 INVENTOR JAMES A. KIPPAN aw United States Patent ()ffice 3,551,280 Patented Dec. 29, 1970 3,551,280 SYNTHETIC TWINES AND METHOD OF PRODUCTION THEREOF James A. Kippan, West Vancouver, British Columbia, Canada, assignor, by mesne assignments, to Delta Rope & Twine Limited, Nassau, Bahamas, a corporation of the Bahamas Continuation of application Ser. No. 441,619, Mar. 22,

1965. This application Apr. 1, 1969, Ser. No. 853,986 Int. Cl. D02g 3/36; B28b 3/20 US. Cl. 161-175 6 Claims ABSTRACT OF THE DISCLOSURE A twine comprising a bundle of longitudinally-extending, oriented synthetic monofilaments, and a thin synthetic bedding casing formed of crushable, compatible material encasing the monofilaments, said casing having been applied to said monofilaments when hot enough to fuse with the outer monofilaments with which it is in contact, and a method of making said twine.

This application is a continuation of Ser. No. 441,619, now abandoned.

This invention relates to synthetic twines, and to meth d of producing these twines.

The term twine is intended to include cords, strings and the like.

An object of the present invention is the provision of synthetic twines, and particularly twines made from polyolefins, which have superior characteristics to any twines heretofore produced.

Another object is the provision of a synthetic twine having a higher proportionate simple knot strength than any synthetic twine heretofore produced.

Further objects are the provision of twines having con sistent characteristics throughout the length thereof, which are virtually rot proof, and exhibit good resistance to ultra violet radiation.

Yet another object is the provision of a method of producing synthetic twines having improved strength and knotting characteristics.

A still further object is the provision of a synthetic twine having monofilaments extending substantially parallel to each other, and including means for retaining the monofilaments in this relationship. v

Heretofore, twines and cords have been produced almost entirely from natural fibres. While these fibres have fulfilled their intended purpose, they are rapidly being replaced by superior synthetic fibres, for example, the rapid increase in usage of polypropylene fibres for rope construction. The natural fibres used in making twines, for example, baler twine, were generally sisal or henequen or a combination thereof. Such fibres are short and stiff and difficult to process with consistency. In Ordinary agricultural twines it is usual to find a strength variation in the twine of up to 40% throughout its length. Because of the wide strength variation in natural fibre twines, they are generally constructed larger than necessary to allow for weak spots which are inherent in their construction. Due to the shortness of natural fibres, twines constructed therefrom must be twisted with reasonable short lay to develop the strength of the fibres. Natural fibres also deteriorate rapidly from rot.

Twines made from monofilaments, including small tapes, of polyolefins, for example linear polyethylene, polypropylene or co-polymers thereof, exhibit more dosirable characteristics than natural fibre twines. Their monofilaments are continuous and of high strength or tenacity. Their strength is consistent within narrow limits and they are virtually rot proof.

The main disadvantage of synthetic fibre twines heretofore produced is that, because of their superior tenacity, they are smaller than the equivalent natural fibre twine. Due to the decrease in diameter and the basic consistency and smooth surface of the individual monofilaments in the synthetic twine, the simple knot strength thereof is poor.

A major amount of twine is consumed in agricultural purpose for the baling of hay. The mechanical knotter of practically all hay balers ties a simple knot.

An example of the present invention is illustrated in the accompanying drawings, in which:

FIG. 1 is an illustration of a simple knot,

FIG. 2 is a perspective view, much enlarged, of a piece of twine constructed in accordance with this invention, and

FIG. 3 is a section taken on the line 33 of 'FIG. 2.

Referring to the drawings, FIG. 1 illustrates a simple twine knot 10 joining two pieces of twine 11 and 12. Twines 11 and 12 form main tension members which are brought together side by side and wound into a circular wrap 15 which is disposed substantially at right angles to the main members 11 and '12.

When the twine is constructed of synthetic monofilaments, portions of the monofilaments of main members 11 and 12 bear directly at .17 on portions of the monofilaments of wrap 15 at approximately right angles and, therefore, in point to point contact, that is, each of the surface filaments of the main members is in point contact with surface monofilaments of the Wrap. As tension is applied to members 11 and 12, the knot tightens and compresses the point to point contact between the filaments. At the same time, the filaments of the main members tend to pull out from the encompassing wrap of the knot. The net result is a generation of high frictional heat at the point to point contact of the monofilaments, the generation of heat at a point will greatly reduce the strength of the monofilament at that point. The combination of the resultant heat generation at a point plus the flattening of the monofilament under pressure at the same point generally causes failure at the point. Because only a portion of the monofilaments can be in contact at any one time, it is this portion that initially fails. Monofilaments immediately adjacent those having failed are next brought into intimate point to point contact, brought under friction and pressure and in turn fail.

Twine manufactured in accordance with the present invention does not have the above-mentioned problem.

The present twine comprises a bundle of synthetic monofilaments extending longitudinally of the twine, and a synthetic casing formed of a material which is compatible with the monofilament material encasing said monofilaments. This eliminates the point to point contact between the monofilaments in the area of a knot. Improved results are attained by fusing the casing to the monofilaments with which it is in contact. The casing, when fused to the monofilaments, tends to equalize the load distribution on the monofilaments at the knot, and the fusing prevents the casing from sliding along the monofilament bundle. Furthermore, the frictional contact area is increased and frictional heat dissipated over an increased area. Therefore, more of the monofilaments areable to assume a greater portion of the tensile load before progressive failure commences. Thus, the strength of a simple knot made with this twine is increased considerably over that of a similar knot made in the prior twine.

The twine is greatly improved if the synthetic casing is formed of a foamed material compatible with the monofilament material. This enables the casing to bed into the knot structure and thereby to eliminate slipping at the knot. The foaming reduces the density of the easing material so that overlapped portions of the latter crush in a knot Without allowing the filaments to cut through the casing. This prevents slippage of the twine in the knot.

If desired, the casing may be interrupted by holes or openings therein, and/or it may have fillers therein, such as hydrocarbon waxes, Wood flour, talc, arbutus or fine sand.

It is desirable to have the monofilaments extend substantially parallel with each other and the longitudinal axis of the twine for strength purposes. This bedding casing fused to some of the monofilaments keeps all of the monofilaments in their proper substantially parallel relationship. Furthermore, the casing can have a pigment in it to provide ultra violet shielding for the monofilaments.

It is preferable to use in this twine, monofilaments that have been stretched or oriented in the manner well known in the industry. The monofilaments are oriented at an average draw of from about 1 to 1 to about 9 to 1 Referring to FIGS. 2 and 3 of the drawings, 25 is a piece of twine made up of a plurality of monofilaments 27 whch may be pre-twisted or disposed substantially parallel to the longitudinal axis of the twine. These monofilaments are preferably made of polyolefin such as, for example, linear high density polyethylene or polypropylene. Encompassing the twine monofilaments is a bedding casing 28 preferably formed of polyolefin, and preferably formed of the same material as the material of filaments 27. Casing 28 is formed while hot around the filaments so that it fuses to each of the monofilaments With which it comes into contact at points 30. It is preferable to use in the bedding casing a compatible material that has been foamed before being applied to the filaments. This causes minute bubbles of gas to form in the bedding material, thereby reducing the density thereof. When the casing is formed of foamed polyolefin, there is better feel or hand to the finished product than would otherwise be the case, and the ability of the casing to bed into a knot without slipping is greatly increased.

Bedding casing 28 can be applied to monofilaments 27 by means of a standard plastic extruder which is common to the plastic industry, and extruded around the monofilaments by means of a standard tube-making crosshead.

The process according to the present invention comprises encompassing a continuous bundle of synthetic monofilaments with a compatible synthetic material which is hot enough to fuse slightly with the monofilaments with which said material comes into contact, but not sufficient materially to reduce the tensile strength of the bundle. As stated above, it is preferable to use polyolefin, such as linear high density polyethylene or polypropylene. The compatible synthetic material forms a bedding casing around the monofilaments. This casing is preferably formed of polyolefin, and is preferably made of the same material as the monofilaments.

The polyolefin bedding casing must be such that it will fuse to monofilaments 27 at points 30 to a slight depth. When polyethylene is used, the bedding casing should be made at a temperature ranging from about 400 F. to about 625 F. to ensure the desired depth of fusion. If polypropylene is used, the temperature should be from about 450 F. to about 650 F.

The method is improved by encompassing the synthetic monofilaments with a foamed bedding of a density of about 0.35 to about 0.70. A polyolefin bedding is improved by using a suitable foaming agent, such as bicarbonate of soda. The bicarbonate of soda is added to the polyolefin bedding in the range of 0.5% to about 3% by weight to reduce the density of the material to a density of from about 0.35 to about 0.70. The bedding should be applied to the exterior surface of the bundle of monofilaments to a thickness that is sufiicient to provide a yieldable bed or body therein but not so thick that it will impede the flexibility of the twine. Bedding thickness of about 0.0005 inch to about 0.006 inch has been found satisfactory. The foaming requirements are about the same for polyethylene and polypropylene.

It has been found that a synthetic twine made of a foamed polyolefin bedding fused to the exterior surface of a bundle of polyolefin monofilaments has a consistent simple knot strength of up to of the ultimate straight tensile strength of the twine. In other Words, the foamed bedding helps to spread the load at the knot more evenly over a larger number of the monofilaments than has heretofore been possible, it dissipates the frictional heat over an increased area, and it greatly reduces slippage as tension is applied to the twine at the knot.

The term monofilament used in this specification and in the following claims is intended to include monofilaments of any desired cross section.

What is claimed:

'1. A twine comprising a bundle of oriented polyolefin monofilaments disposed substantially parallel to the longitudinal axis of the twine, and a thin polyolefin casing formed of foamed and crushable material encasing said monofilaments and fused to the outer monofilaments of the bundle with which it is in contact, said polyolefin casing being extruded onto said bundle at a temperature of about 400 to 650 F., said temperature being hot enough to fuse the foamed casing with the monofilaments with which it comes into contact without materially reducing the tensile strength of the bundle, said foamed casing having a density of about 0.35 to 0.70 and a thickness of about 0.0005 to 0.006 inch.

2. The twine of claim 1 wherein the monofilaments and the foamed casing are formed of polypropylene.

3. The twine of claim 1 wherein the monofilaments and the foamed casing are formed of polyethylene.

4. A method of producing synthetic twines which comprises extruding onto a continuous bundle of oriented monofilaments of polyolefin a thin foamed and crushable casing of polyolefin at a temperature of about 400 F. to 650 F., said temperature being hot enough to fuse the foamed casing with the monofilaments with which said casing comes into contact without materially reducing the tensile strength of bundle, and said casing having a density of about 0.35 to 0.70 and a thickness of about 0.0005 to 0.006 inch.

5. The method of claim =4 wherein the bundle of oriented monofilaments and casing are formed of polyethylene.

6. The method of claim 4 wherein the bundle of oriented monofilaments and casing are formed of polypropylene.

References Cited UNITED STATES PATENTS 3,091,017 5/1963 Wetterau 2875 8,210,446 .10/ 1965 Yamakawa et a1. 264-47 3,315,454 4/ 1967 Carranza 57140 3,315,455 4/1967 Stoller 57-144 ROBERT F. BURNETT, Primary Examiner R. L. MAY, Assistant Examiner US. Cl. X.R. 

